A seat reclining device is known which includes a gear differential transmission mechanism for adjusting the opening angle of a hinge through which the seating portion and the backrest portion are coupled together, whereby the inclination angle of the backrest of the seat is adjustable.
A gear differential transmission mechanism in a conventional seat reclining device is described mainly with reference to FIG. 5 and partly with reference to FIG. 1. In this arrangement, the hinge through which the seating portion and the backrest of the seat are coupled together is provided with the gear differential transmission mechanism.
This differential transmission mechanism includes an internal gear 1 (see FIG. 1), and an external gear 2 having a smaller number of teeth than the internal gear and meshing with the internal gear. An arcuate gap is defined between a ring-shaped bearing bush 10 and a shaft 4 of the internal gear 1 and its slide bearing 11. A pair of wedge-shaped pieces 6 and 6′ are received in the arcuate gap such that their respective narrow ends 6a and 6′a face in opposite directions to each other. A compression coil spring 7 is also received in the arcuate gap and biases the wedge-shaped pieces away from each other.
In this arrangement, when the wedge-shaped pieces 6 and 6′ slide in the arcuate gap by operating the slide bearing 11 and its protrusion 11a, the external gear 2 is configured to separate from the internal gear 1, thereby making it possible to adjust the inclination angle of the backrest.
Such a differential transmission mechanism is also known as a Taumel mechanism. A reclining seat device for an automotive seat including this mechanism is provided with the bearing bush 10 in the external gear 2 as described above. The wedge-shaped pieces 6 and 6′ are configured to be brought into frictional sliding contact with the bearing bush 10 (Patent documents 1 and 2).
In the reclining device of the type in which the wedge-shaped pieces 6 and 6′ are brought into frictional sliding contact with the bearing bush 10, it was necessary to press the bearing bush 10 into the external gear 2 for smooth movement of the wedge-shaped pieces 6 and 6′.
Such a bearing bush 10 has a sliding surface made of a resin having good sliding properties, and is sometimes also called a winding bush. It has e.g. a laminate structure as shown in FIG. 4. That is, the bush shown in FIG. 4 is a laminated slide bearing comprising a back metal plate 10a, a porous sintered layer 10b superposed on the back metal plate, and a resin layer 10c comprising a resin composition having sliding properties and partially filling the pores of the porous sintered layer 10b. 
Patent document 1: JP Patent publication 3-237904A
Patent document 2: JP Patent publication 2004-33401A